Constrained complexes of manganese(II) tetraphenylporphyrin in rigid solution

Konishi, Shiro; Hoshino, Mikio; Imamura, Masashi

doi:10.1021/j100397a039

Cited by 15 publications

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“…Although Mn(III) porphyrins are paramagnetic with a high spin d 4 configration, they are “ESR silent” at conventional fields and frequencies due to short spin–lattice relaxation times and large zero-field splittings. − The currently investigated manganese(III) butano- and benzoporphyrins also showed no ESR signal under the given experimental conditions. However, the Mn(II) butano- and benzoporphyrins prepared by chemical reduction exhibit typical Mn(II) ESR signals over a wide range of magnetic fields.…”

Section: Resultsmentioning

confidence: 95%

“…In each case, the spectra are comprised of two resonances, one located at g ⊥ = 5.6–5.8 and the other at g // = 2.0, with a six line hyperfine splitting from the 55 Mn nucleus ( I = 5/2), giving the characteristic of a high-spin (3d 5 , S = 5/2) configuration of Mn(II) porphyrins. − …”

Section: Resultsmentioning

confidence: 99%

“…It is known that the ligand binding to the Mn(II) porphyrin has a significant effect on the ESR properties of the compound. The four-coordinate (TMP)Mn II (TMP = tetramesitylporphyrin) only has a distinct resonance at g // ≈ 2.0, while five-coordinate imidazole-bound Mn(II) porphyrins have a strong resonance at g ⊥ ≈ 5.9 and a weak signal at g // ≈ 2.0. − …”

Section: Resultsmentioning

confidence: 99%

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Spectral, Electrochemical, and ESR Characterization of Manganese Tetraarylporphyrins Containing Four β,β′-Pyrrole Fused Butano and Benzo Groups in Nonaqueous Media

Fang

Wang

et al. 2019

Inorg. Chem.

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Two series of β,β′-pyrrole butano- and benzo-substituted mangenese(III) tetraarylporphyrins were synthesized and characterized with regard to their spectral and electrochemical properties. The investigated compounds have the general formula butano(Ar)4PorMnCl and benzo(Ar)4PorMnCl, where Por is the dianion of the porphyrin and Ar is a p-CH3Ph, Ph or p-ClPh group on each of the four meso-positions of the macrocycle. Each manganese(III) butano- or benzoporphyrin was examined in CH2Cl2 and/or pyridine containing 0.1 M tetra-n-butylammonium perchlorate and the data then were compared to that of the parent tetraarylporphyrins having the same meso-substituents. Up to four reductions are observed for each compound, the first being metal-centered to generate a Mn(II) porphyrin, and the second and third being porphyrin ring-centered to give a Mn(II) porphyrin π-anion radical and dianion, respectively. The one-electron reduced manganese porphyrins have an ESR spectrum with signals at g ⊥= 5.6–5.8 and g // = 2.0, indicating a mixture of the four- and five-coordinated Mn(II) complexes in a high-spin state (3d5, S = 5/2, I = 5/2). Data from cyclic voltammetry and spectroelectrochemistry both suggest that formation of the porphyrin dianion is followed by a chemical reaction at the electrode surface to give an electroactive phlorin anion. The effects of solvent and porphyrin substituents on ultraviolet–visible light (UV-vis) spectra, redox potentials, and electron transfer mechanisms are discussed.

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Section: Resultsmentioning

confidence: 95%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Spectral, Electrochemical, and ESR Characterization of Manganese Tetraarylporphyrins Containing Four β,β′-Pyrrole Fused Butano and Benzo Groups in Nonaqueous Media

Fang

Wang

et al. 2019

Inorg. Chem.

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“…Mn II TPP in toluene was produced by photochemical reduction of ClMn III TPP in the presence of benzophenone. Benzophenone undergoes photochemical hydrogen abstraction from a toluene molecule to give the ketyl radical, which was found to reduce Mn III TPP(Cl), resulting in the formation of Mn II TPP, e.g., The ESR measurements of the product at 77 K confirmed the formation of Mn II TPP …”

Section: Resultsmentioning

confidence: 99%

Laser Flash Photolysis Studies of Nitritomanganese(III) Tetraphenylporphyrin. Reactions of O₂, NO, and Pyridine with Manganese(II) Tetraphenylporphyrin

Hoshino¹,

Nagashima²,

Seki³

et al. 1998

Inorg. Chem.

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Laser photolysis of nitritomanganese(III) tetraphenylporphyrin, MnIIITPP(ONO) (1), in degassed toluene gives manganese(II) tetraphenylporphyrin, MnIITPP (2), plus NO2. The quantum yield, Φ, for the formation of MnIITPP is dependent on the excitation wavelength: Φ = 0.045 at 355 nm and Φ = 0.0064 at 532 nm. Continuous photolysis studies reveal that the quantum yield for the net photodecomposition of 1 is much smaller (10-4). Thus, MnIITPP produced by laser photolysis of MnIIITPP(ONO) mostly returns to 1 by recombination with NO2 according to second-order kinetics with a rate constant 2.2 × 109 M-1 s-1. The kinetics for the reactions of MnIITPP with O2, NO, and pyridine were investigated in detail. In aerated toluene, MnIITPP reversibly reacts with oxygen to yield the dioxygen adduct, MnTPP(O2) (3). The rate constants, k f(O2) and k b(O2), for the formation and dissociation of 3 at 300 K were determined to be 1.93 × 107 M-1 s-1 and 9.0 × 104 s-1, respectively, and the equilibrium constant, k f(O2)/k b(O2), is therefore 2.1 × 102 M-1. MnIITPP reacts with pyridine to give MnIITPP(Py) with a rate constant of 9.5 × 108 M-1 s-1. MnIITPP reacts with NO to yield nitrosylmanganese porphyrin, MnIITPP(NO), with the rate constant 5.3 × 108 M-1 s-1. The association reactions of MnIITPP with NO, pyridine, O2, and NO2 are discussed in comparison with those of other metalloporphyrins.

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“…The differences in peak shape shown in Figure 8 b are due to differential axial ligation. Compound 15 is formed by photocleavage of the Mn−N bond and thus has no axial ligand, whereas independently synthesized 15 has an axial THF ligand [31b] . The observed EPR features were insensitive to the photolysis matrix: Photolysis of a solvent‐free thin film of 13 a resulted in the evolution of an EPR spectrum of 15 (Figure S14).…”

Section: Resultsmentioning

confidence: 99%

Nitrene Photochemistry of Manganese N‐Haloamides**

et al. 2021

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Manganese complexes supported by macrocyclic tetrapyrrole ligands represent an important platform for nitrene transfer catalysis and have been applied to both C−H amination and olefin aziridination catalysis. The reactivity of the transient high‐valent Mn nitrenoids that mediate these processes renders characterization of these species challenging. Here we report the synthesis and nitrene transfer photochemistry of a family of MnIII N‐haloamide complexes. The S=2 N‐haloamide complexes are characterized by 1H NMR, UV‐vis, IR, high‐frequency and ‐field EPR (HFEPR) spectroscopies, and single‐crystal X‐ray diffraction. Photolysis of these complexes results in the formal transfer of a nitrene equivalent to both C−H bonds, such as the α‐C−H bonds of tetrahydrofuran, and olefinic substrates, such as styrene, to afford aminated and aziridinated products, respectively. Low‐temperature spectroscopy and analysis of kinetic isotope effects for C−H amination indicate halogen‐dependent photoreactivity: Photolysis of N‐chloroamides proceeds via initial cleavage of the Mn−N bond to generate MnII and amidyl radical intermediates; in contrast, photolysis of N‐iodoamides proceeds via N−I cleavage to generate a MnIV nitrenoid (i.e., {MnNR}7 species). These results establish N‐haloamide ligands as viable precursors in the photosynthesis of metal nitrenes and highlight the power of ligand design to provide access to reactive intermediates in group‐transfer catalysis.

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Constrained complexes of manganese(II) tetraphenylporphyrin in rigid solution

Cited by 15 publications

References 0 publications

Spectral, Electrochemical, and ESR Characterization of Manganese Tetraarylporphyrins Containing Four β,β′-Pyrrole Fused Butano and Benzo Groups in Nonaqueous Media

Spectral, Electrochemical, and ESR Characterization of Manganese Tetraarylporphyrins Containing Four β,β′-Pyrrole Fused Butano and Benzo Groups in Nonaqueous Media

Laser Flash Photolysis Studies of Nitritomanganese(III) Tetraphenylporphyrin. Reactions of O₂, NO, and Pyridine with Manganese(II) Tetraphenylporphyrin

Nitrene Photochemistry of Manganese N‐Haloamides**

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Constrained complexes of manganese(II) tetraphenylporphyrin in rigid solution

Cited by 15 publications

References 0 publications

Spectral, Electrochemical, and ESR Characterization of Manganese Tetraarylporphyrins Containing Four β,β′-Pyrrole Fused Butano and Benzo Groups in Nonaqueous Media

Spectral, Electrochemical, and ESR Characterization of Manganese Tetraarylporphyrins Containing Four β,β′-Pyrrole Fused Butano and Benzo Groups in Nonaqueous Media

Laser Flash Photolysis Studies of Nitritomanganese(III) Tetraphenylporphyrin. Reactions of O2, NO, and Pyridine with Manganese(II) Tetraphenylporphyrin

Nitrene Photochemistry of Manganese N‐Haloamides**

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Laser Flash Photolysis Studies of Nitritomanganese(III) Tetraphenylporphyrin. Reactions of O₂, NO, and Pyridine with Manganese(II) Tetraphenylporphyrin